Glycerin suppositories are the best starting point for most people with constipation. They’re available over the counter, work within 15 to 30 minutes, and cause fewer side effects than stronger options. But if glycerin doesn’t do the job, bisacodyl suppositories are a more powerful alternative that works through a different mechanism. The right choice depends on how severe your constipation is, how quickly you need relief, and whether you’re dealing with a one-time issue or a recurring pattern.
How Glycerin Suppositories Work
Glycerin is a hyperosmotic agent, which means it pulls water into the lower bowel. This softens stool sitting in the rectum while also stretching the rectal wall enough to trigger the natural urge to go. It’s a gentle, localized effect that doesn’t reach deeper into the colon. Most people have a bowel movement within 15 to 30 minutes of insertion.
Because glycerin works locally and doesn’t get absorbed into the bloodstream in any meaningful way, it has an excellent safety profile. The Merck Manual lists no adverse effects for glycerin suppositories even in infants and young children, making it one of the few constipation remedies considered appropriate across all age groups. For children under two, a half to one pediatric-sized suppository is the standard approach. Kids six and older can use the adult size.
The main limitation of glycerin is that it only addresses stool already in the rectum. If the problem is higher up in the colon, or if your constipation involves slow-moving stool throughout the large intestine, glycerin may not be enough.
How Bisacodyl Suppositories Work
Bisacodyl is a stimulant laxative that takes a more aggressive approach. Once inserted, enzymes in the colon break it down into an active compound that does two things simultaneously: it stimulates nerve endings in the colon wall to trigger strong, wave-like contractions (peristalsis), and it reduces the colon’s absorption of water so stool stays softer and moves more easily. The result is both increased movement and increased fluid in the bowel.
In a head-to-head comparison studying children with constipation, bisacodyl triggered the strong contractions needed for a bowel movement in 95.5% of patients, compared to 86.4% for glycerin. All four patients who didn’t respond to glycerin did respond to bisacodyl. The median time to those contractions was about 7 minutes for bisacodyl and 2.5 minutes for glycerin, though the overall time to a complete bowel movement is similar for both, typically in the 15 to 30 minute range.
Bisacodyl’s stronger stimulation comes with a tradeoff. It’s more likely to cause cramping, rectal irritation, or a burning sensation. Some people experience urgency that’s hard to control. These effects are usually mild and short-lived, but they make bisacodyl a second-line choice for most situations rather than something to reach for first.
Carbon Dioxide-Releasing Suppositories
A third, less well-known option releases carbon dioxide gas once inserted. The gas gently stretches the rectal wall, mimicking the natural distension that signals your body it’s time for a bowel movement. This triggers peristalsis without any chemical stimulation of the intestinal lining.
A randomized, placebo-controlled trial found these suppositories effective for chronic functional constipation. Their biggest advantage is safety in vulnerable populations. Because they don’t affect fluid balance or electrolyte levels, they may be a better fit for older adults or people with kidney or heart conditions where electrolyte shifts are a concern. They’re less widely available than glycerin or bisacodyl, and you may need to ask a pharmacist to help locate them.
Choosing the Right One for Your Situation
For occasional constipation where stool feels ready but just won’t pass, glycerin is the clear first choice. It’s the mildest option, works quickly, and is safe for nearly everyone including young children and pregnant women.
Switch to bisacodyl if glycerin hasn’t worked after a reasonable try, or if your constipation is more stubborn. Bisacodyl is also the better option when you suspect the slowdown isn’t limited to the rectum, since its effects reach further into the colon. Many people with chronic constipation find that bisacodyl is the only suppository that reliably produces results.
Consider carbon dioxide suppositories if you need something gentler than bisacodyl but more effective than glycerin, or if you have a medical condition that makes electrolyte balance a concern.
How to Use a Suppository Effectively
Lie on your left side with your lower leg straight and your upper knee bent toward your chest. This position aligns with the natural curve of the lower bowel. Unwrap the suppository and insert it pointed end first, pushing it about an inch past the opening. In children, use a pinky finger and insert only about half an inch.
After insertion, close your legs and remain lying down or sitting still for 15 to 30 minutes. This gives the suppository time to melt fully and start working. Moving around too soon or trying to use the toilet immediately can cause the suppository to slip out before it’s had any effect. You’ll feel a growing urge during this waiting period, which is the suppository doing its job.
If you experience rectal bleeding, blistering, or pain that wasn’t there before using the suppository, stop using it. Some mild warmth or slight burning with bisacodyl is normal, but sharp pain is not.
Suppositories vs. Oral Laxatives
Suppositories work faster than any oral laxative because they act directly where the problem is. An oral stimulant laxative typically takes 6 to 12 hours. An oral osmotic laxative can take one to three days. A suppository works in under 30 minutes. This makes suppositories the better choice when you need relief now, not tomorrow morning.
The flip side is that suppositories only treat the end of the pipeline. If your constipation is caused by slow transit through the entire colon, a poor diet, dehydration, or medication side effects, a suppository will clear what’s in the rectum but won’t address the upstream problem. For recurring constipation, oral options like fiber supplements or osmotic laxatives taken daily are generally more effective as a long-term strategy, with suppositories reserved for breakthrough episodes when things get backed up despite your regular routine.
When Suppositories Aren’t the Right Call
Suppositories should not be used if you have severe abdominal pain that you can’t explain, a visibly swollen abdomen that doesn’t go down, vomiting, or a complete inability to pass both stool and gas. These can be signs of a bowel obstruction, where stimulating the intestine could make things significantly worse. Rectal bleeding from an unknown source is another reason to hold off and get evaluated first.
Using stimulant suppositories like bisacodyl daily for weeks on end is generally not recommended. While the older idea that stimulant laxatives permanently “damage” the bowel has been largely debunked, relying on them regularly without addressing the underlying cause means you’re treating the symptom while the root problem continues. If you find yourself needing a suppository more than a few times a month, that pattern itself is worth investigating.